Long band life wheel-band casting machine

ABSTRACT

A machine for continuously casting metal wherein an endless flexible band is guided into closed relationship with a portion of the peripheral groove of a rotatable casting wheel by a plurality of band guide wheels of substantially the same diameter, and a band positioning wheel of smaller diameter than the band guide wheels is positioned adjacent the periphery of the rotatable casting wheel and is arranged to press the flexible band into positive contact with the casting wheel. The ratio between the thickness of the flexible band and the diameter of the smaller band positioning wheel is such that no more than three times the bending strain is applied by the smaller band positioning wheel to the flexible band than the strain applied by the other band guide wheels.

United States Patent John 11. Murphy Atlanta, Ga.

Jan. 28, 1970 Aug. 3, 1971 Southwire Company Carrollton, Ga.

inventor Appl. No. Filed Patented Assignee 11.5. CI. 164/278 Int. Cl 822d 11/06 Field 01 Search 164/82, 87, 89,278,281

References Cited UNITED STATES PATENTS 6/1967 Cofer Primary Examiner-R. Spencer Annear Attorney-Jones and Thomas ABSTRACT: A machine for continuously casting metal wherein an endless flexible band is guided into closed relationship with a portion of the peripheral groove of a rotatable casting wheel by a plurality of band guide wheels of substantially the same diameter, and a band positioning wheel of smaller diameter than the band guide wheels is positioned adjacent the periphery of the rotatable casting wheel and is arranged to press the flexible band into positive contact with the casting wheel. The ratio between the thickness of the flexible band and the diameter of the smaller band positioning wheel is such that no more than three times the bending strain is applied by the smaller band positioning wheel to the flexible band than the strain applied by the other band guide wheels.

Patented Aug. 3, 1971 3,596,705

3 Sheets-$heet 1 INVENTOR JOHN H, MURPHY Patented Aug. 3, 1971 RAIN o: STRAIN STRAIN 3 Sheets-Sheet 2 OOTI lo-0035 all I 4 F1 6 FIGS Patented Aug. 3, 1911 3,596,705

3 Sheets-Shoot 8 INVEHTOR JOHN H. MURPHY 'BAND THICKNESS t ATTORNEYS LONG BAND LIFE WHEEL-BAND CASTING MACHINE BACKGROUND OF THE INVENTION In a typical system for continuously casting metal. such as copper, steel or aluminum, an endless flexible metal band is guided about a portion of the peripheral groove of a rotatable casting wheel, and molten metal is poured into the moving mold formed by the band the peripheral groove in the wheel. As the casting wheel rotates, coolant is applied to its external surfaces and to the outside surface of the portion of the band that closes the peripheral groove of the casting wheel to extract the heat from the molten metal at a rapid rate and to prevent the casting wheel and band from overheating. By the time the metal band is removed from the peripheral groove of the casting wheel by the band wheels, the molten metal will have been solidified and can be extracted from the casting wheel and passed on to another stage in the continuous process.

The function of the band guide wheels is to guide the band into engagement with the periphery of the casting wheel to form the arcuate mold, and then to remove the band from the periphery of the casting wheel to open the mold, and guide the band back to its initial mold forming position. One arrangement is to have a single large tensioning wheel spaced above the casting wheel and have the inner surface of the flexible band extend about both the casting wheel and the tensioning wheel. The other typical arrangement is to have the band pass beneath the casting wheel during its return flights, with the band guide wheels engaging the outer" surface of the band. In both arrangements it is desirable to guide the band away from the area above the casting wheel so that the equipment necessary for pouring the molten metal into the mold and extracting the solidified metal from the mold can be positioned in this space. Thus, the tensioning wheel or band guide wheels must be sized and positioned to guide the band away from the upper portion of the casting wheels; however, in order that the band be guided away from the upper portion of the casting wheel, it has been found necessary to utilize a relatively small band presser wheel or band positioning wheel to position the band adjacent the casting wheel and urge the band into its initial engagement with the periphery of the casting wheel. The band positioning wheel is of small diameter in order to keep the area above the casting wheel relatively free from encumbrance by the band.

In the operation of a continuous casting machine f the types generally set forth above, one of the major maintenance problems is the care and replacement of the band. It is necessary that the band be of relatively small thickness so that it can bend and flex as it passes around the casting wheel and band wheels. Also, a relatively thin band transfers the heat from the molten metal more rapidly than a thicker band and allows the molten metal to solidify more rapidly; however, the relatively thin band is more likely to become overheated from the transfer of heat from the molten metal and deteriorate more rapidly than a relatively thick band. Thus, the endless flexible metal band utilized with a continuous metal casting machine must be fabricated with a thickness to withstand substantial heat deterioration, and yet be thin enough to flex around the band wheels. The continual bending and flexing of the band about the smaller band positioning wheel has the most damaging effect on the band since the hand must undergo a curvature of a shorter radius when passing around this band wheel, and the strain felt by the band from the smaller band wheel tends to rapidly deteriorate the band.

SUMMARY OF THE INVENTION strain felt by the band material as it passes around the band positioning wheel during each cycle of the band. While the diameters of the larger band guide wheels are sufficiently large to prevent excessive strain in the band as it passes over these guide wheels, the band positioning wheel next adjacent the casting wheel which urges the band into engagement with the casting wheel at the pouring spout has been enlarged so that the strain experienced at this location is no more than three times the strain experienced at the other band wheels.

Thus, it is an object of this invention to provide a casting machine for continuously casting metal which includes a band and band wheel arrangement that extends the life of the band over the previously known casting machines.

Another object of this invention is to provide a casting machine for continuously casting metal that requires less maintenance than the prior art.

Other objects, features and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a casting machine for continuously casting metal wherein the inner surface of the band is passed around the casting wheel and a tension wheel, and the outer surface of the band is engaged by a smaller band positioning wheel.

FIGS. 2 and 3 are graphs which illustrate band strain of the band of the casting machine of FIG. 1; FIG. 2 illustrating band strain with the use of a relatively small band positioning wheel, and FIG. 3 illustrating band strain with the use of a relatively large band positioning wheel.

FIG. 4 is a schematic illustration of a casting machine for continuously casting metal wherein the band is guided with its inner surface engaging the casting wheel and its outer surface passing around the band wheels.

FIGS. ,5 and 6 are graphs similar to those of FIGS. 2 and 3 and illustrate band strain of the band of the casting machine of FIG. 4; FIG. 5 showing band strain when a relatively small band positioning wheel is used. and FIG. 6 illustrating band strain when a larger band. positioning wheel is used.

FIG. 7 is a schematic detail illustration of the intersection of the band with the casting wheel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in more detail to the drawing. in which like numerals indicate like parts throughout the several views. FIG. 1 shows a casting machine 10 which includes casting wheel 11., hand tension wheel 12, and band positioning wheel 13. Continuous flexible band 14 extends around casting wheel 11 and band tension wheel 12 an forms an arcuate mold with the peripheral groove (not shown) of casting wheel 11. Band positioning wheel 13 urges band 14 into engagement with the periphery of casting wheel 11. I

The graphs of FIGS. 2 and 3 represent band strain as the continuous flexible band 14 passes through a cycle about casting wheel 1-1 and band tension wheel 12. The numbered points along the abscissas of the graphs illustrate the corresponding numbered positions about the casting machine, and the ordinates of the graphs illustrate the amount of strain felt by the band. The difference between FIGS. 2 and 3 is the amount of strain felt by the band at point 3 in the band cycle. where a larger band positioning wheel 13 is used for the cycle of the graph of FIG. 3, and a smaller band positioning wheel 13 was used for the cycle of the graph of FIG. 2.

FIG, 4 shows casting machine 20 which includes casting wheel 21. band guide wheels 22, 23, 24, and 25, hand positioning wheel 26, and endless flexible metal band 27. The inner surface of band 27 extends about casting wheel 21 and defines a mold with the peripheral groove (not shown) of the casting wheel. The outer surface of band 27 extends about band guide wheels 2225, and about band positioning wheel 26.

FIGS. and'6 are graphs of the strain felt by band 27 as it passes through a cycle about casting machine 20.- As with FIGS. 2 and 3, the positions indicated along the abscissas of the graphs of FIGS. 5 and 6 indicate the various corresponding positions noted in FIG. 4 in a single band cycle, withthe difference in FIGS. 5 and 6 being that a larger band positioning wheel 26 was used for the cycle of the graph of FIG. 6 while a smaller band positioning wheel was used for the'cycle of the graph of FIG. 5. f

In both FIGS. 1 and 4 the illustrations are schematic andthe relative sizes of the elements of the casting machines arenot to scale, particularly the sizes of band positioning wheels 13 and 26. Furthermore, it will be apparent from FIGS.'2, 3, 5, and 6 that the sizes of band positioning wheels 13 and'26 are variable for the purpose of illustrating the disclosed invention.

The continuous metal bands 14 and 27 4 where flexible, and as with any material they are subject to failure due to fatigue from continuous flexing as the bands pass around the various band wheels and due to the thermal shock experienced in each cycle of the band from the heat exchange from the molten metal poured into the arcuate mold formed between the band and the casting wheel. When the bands are bent about the casting wheel orv one of the guide wheels, the theoretical strain setup in the band surface is e=( where t is the band thickness and l) is the wheel diameter. The strain is in the tension on the outside or convex surface of the band and the compression on the inside or concave surface of the band next to the wheel about which it is passing. Of

strain due to the heat gradient across the thickness of the band will depend on the rate of heat transfer through the band, and

on the ability of the band to deform. As is shown in FIG. 7, the

molten metal 30 initially contacts band 14 when the band is relatively cool and immediately heats band 14 to its highest temperature thus causing a substantial thermal shock. The temperature gradient is illustrated at 31. Of course, the increased temperature causes the band to expand lengthwise, and since the surface of the band in direct contact with the molten metal is hotter than the outer surfaceof the band, the inner surface will tend to expand more than the outersurface. If the band were not under tension and extended about the casting wheel, it would normally bend away from the casting wheel. Thus, in order to extend the band around the cur ature of the casting wheel a substantial bending strain is exerted in the band. The bending strain will be proportional to the difference in band surface temperature and band average temperaturc. To illustrate the conditions of a band extending about a casting wheel with its inner surface in contact with molten metal and its outer surface having coolant applied to it, the thermal strain can be assumed to be the same as that f a band of twice the thickness of band l4, thermal shocked on both sides and cool in the center. A band under these conditions would not bend and would have the same difference between surface and center temperatures as the inner and outer surface temperatures of band l4.

To determine the bending strain ofthe band, the maximum thermal stress at the surface is:

where a" is a dimensionless stress and is gi en by:

(fl w/E a i -Tm) G"=-(/a( TLTTTIJ) where B is the Blot number. E is the modulus of elasticity, a is thethermal expansion coefficient. (T rT is the temperature difference between the molten metal and the band, It is the surface heat transfer coefficient, k is the band thermal conductivity, r is the band thickness.

B=(h(2r)/k) For an example of a steel band and molten copper:

Taking a as 6.5 I0 in/in. F. and (T -T as 2000 F., we have:

e,,,,, ,.=0.0038 ir'ifin. This is a compressive thermal strain set up in the band surface adjacent the molten copper and is assumed to be approximately the same for all casting machines.

To estimate band life on a casting machine, reference is made to FIGS. 1 and 2 of the drawing where a band cycle is plotted. Point 0 is the beginning point of the graph of FIG. 2 and the point on the band after it has left the casting wheel. As the band travels around the machine, it undergoes various bending strain conditions as illustrated at the other point of the figures. At point 1, the strain is given by (!/D). where 1- /0 inches and D=55 inches, and as illustrated on the graph of FIG. 1, is 0.0023 inch per inch. The remaining portion of the graph of FIG. 2 plots the strain experienced by the band as it travels through one band cycle back toward the 0 position. It will be noted that a relatively small strain is felt by the band at position I, while a relatively large strain is felt at position 3. Positions I and 3 are located in the middle of the curvature of the band as it Passes about tension wheel 12 and band positioning wheel 13, and a graphic presentation is made of band strain at these positions. Position 4 on the graph indicates strain of the band due to the thermal gradient across the band added to band bending strain due to bending the band around the curvature of the casting wheel; the band strain due to its curvature being illustrated by the dashed line.

Theoretically. each band can pass around the wheels of a casting machine a certain number of times before it fails. This is called band life. and a relationship has been established between the strain felt by a band during each cycle and its life. If n, represents the number of times a certain strain occurs in a band cycle. and N, is the life associated with this strain range. we can determine the number of band cycles. N. to failure:

For example, in casting machine 10 of FIG. 1 the strain of 0.0023 occurs once, the strain of 0.021 occurs once. and the st ain of 0.006 occurs once. The band life associated with each of these strains. is respectivclY:

2X10 cycles. 7.5 l0 cycles. 10 cycles.

Therefore, the number of band cycles to failure are:

Since band failure as calculated above is for complete freeture of the material and it is expected that visible cracks in the band will appear long bef re the band fractures, under normal situations the band will be removed from the casting machine before its fracture.

It is acknowledged that there are various other parameters that should be considered for an absolutely accurate determination of band life. For instance, the temperature of the molten metal will vary, the rate of cooling of the casting wheel and band is determined by coolant volume and temperature and will vary, the tension applied to the band material and the length of the band will vary, the width of the band and the portion of the band that does not come into contact with the molten metal may vary, and there will be variations in the thickness of the band. These and other varying parameters are likely to be present in every casting machine; but for our purposes, we have merely established a relationship between band life and the bending of the band As illustrated by the data in FIGS. 2 and 3, when band positioning wheel 13 is 6 inches in diameter and the band thickness is one-eighth inches, the coefficient of strain, e=r/l) is 0.021 whereas, when band positioning wheel 13 has a diameter of 20 inches, the coefficient of band strain is only 0.0062 when using the same one-eighth inch band. Thus, since the reduction of band strain in each band cycle extends band life, the use of a larger diameter band positioning wheel 13 functions to extend the life of band 14. Similarly, if the thickness of band 14 was reduced, band life would also be extended. Thus, to extend band life, the ratio between band thickness and wheel diameter must be as low as practical in keeping with heat deterioration problems previously discussed.

A comparison of the graphs of FIGS. 5 and 6 also disclosed that the use of a larger band positioning wheel 26 in casting machine 20 reduces band strain, and increases band life. FIG. 5 illustrates data for a band positioning wheel 26 of a diameter of 6 inches and a band thickness of one-eighth inch. FIG. 6 illustrated data for the same casting machine but with a band positioning wheel 26 having a diameter of i2 inches and a band thickness of one-eighth inch. While the strain at position 9 in the band cycle is 0.021 for the smaller band positioning wheel 26, the strain is only 0.0104 for the larger band positioning wheel. Obviously, the band life will be prolonged with the use of the larger band positioning wheel 26.

To extend band life, it would be desirable to form band positioning wheels 13 and 26 with diameters as large as the band tensioning wheel 12 or band guide wheels 22-25; however, the space requirements above casting wheels 11 and 21 require that smaller diameter band positioning wheels be utilized. Thus, while the strain encountered in the bands at positions 3 (FIG. 1) and 9 (H0. 4), must necessarily be in excess of the strains in the band as the band passes around band guide wheels 22-25 and band tensioning wheel 12, it is desirable to hold the strain encountered in the band to a level no greater than the strain in the band as the band contacts the molten metal, so the band thickness and materials can be selected and gauged for only the highest necessary strain in a single cycle of the band. Since band stain virtually cannot be reduced through a level below that encountered in positions 4 (FIG. 1) and (FIG. 4), it is unnecessary to enlarge the diameters of band positioning wheels 13 and 26 to hold the strain below the necessarily high strain level since i'urther enlargement of the band positioning wheels would cause the wheel to occupy an excessive amount of space above the casting wheel.

This band strain limits for the band positioning wheels for the examples shown are calculated:

e=(!/D) 1/90). The band thicknesses are between approximately 0.074? inch and 0.125 inch, and the band positioning wheels are 12 inches and larger for casting machines of the type illustrated in FIG. s and inches and larger for the casting machines of the type illustrated in FIG. 1. The diameter of the guide wheels of the FIG. 4 cutting machines were 36 inches and the diameter oi the tensioning wheel oi the FlG. l casting machine was 60 inches. Thus, the ratio between positioning wheel diameter and guide wheel diameter and guide wheel or tensioning wheel diameter is maintained at one to three. This ratio is suitable since approximately three times the amount of band strain is experienced when the band first encounters the molten metal as is experienced when extending about a guide wheel.

While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

lclaim:

1. in a machine for continuously casting metal wherein an endless flexible band is guided into closed relationship with a portion of the peripheral groove of a rotatable castin wheel, guided away from the peripheral groove, and returne on the same side of the casting wheel to the peripheral groove by a plurality of band guide wheels of substantially the same diameter and a band positioning wheel of smaller diameter than the band guide wheels is positioned adjacent the periphery of the rotatable casting wheel and arranged to press the flexible band into positive contact with the casting wheel, the improvement therein of the ratio between the thickness of the flexible band and the diameter of the band positioning wheel being lower than one'to 90.

2. The invention ofclaim l and wherein the thickness ofthe flexible band is in the range of from 0.0747 inch to 0.125 inch, and the diameter of the band positioning wheel is greater than 12 inches.

3. The invention of claim 1 wherein the diameter of band positioning wheel is at least one-third as large as the diameter of the band guide wheels.

4. The invention of claim 1 wherein the diameter of the band positioning wheel is sized to impart no more than three times the bending strain to the flexible band than the band guide wheels.

5. The invention of claim 1 wherein the diameter of the band positioning wheel is sized to impart no more bending strain to the flexible band than the strain felt by the band as it passes about the casting wheel and is in direct contact with molten metal.

6. in a machine for continuously casting metal wherein the inner surface oi an endless flexible band partially about the peripheral groove of a casting wheel and about a tensioning wheel spaced from the casting wheel and a band positioning wheel is placed adjacent the casting wheel and engages the outer surface of the band urges the inner surface of the band into engagement with the casting wheel, the improvement therein of the ratio of band thickness to band positioning wheel diameter being smaller than one to 90.

7. The invention of claim 6 wherein the band tensioning wheel diameter is greater than three times the positioning wheel diameter.

8. The invention of claim 6 wherein the band positioning wheel is sized and arranged to impart no more than three times the bending strain to the flexible band than the tensioning wheel.

9. The invention of claim 6 wherein the diameter of the and positioning wheel is sized to impart no more strain to the flexible hand than the strain felt by the band as it passes about the casting wheel and is in direct contact with molten metal.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,596,705 Dated Auqust 3, 1971 Inventor(s) John H Murghy It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 6, line 2 (column 6, line numbered 41) after "flexible band" insert extends Claim 6, line 6 (column 6, line numbered 45) after "band" insert -and-;

Claim 9 line 1 (column 6 line numbered 56) change "and" to -band-.

Signed and sealed this 8th day of February 1972.

(SEAL) Attest:

EDWARD M.FLETCH5R,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC SCENE-P59 JRM PO-105O (10-69) a u s. aovsmmem Fmm'mc orncawas o-sss-sn 

1. In a machine for continuously casting metal wherein an endless flexible band is guided into closed relationship with a portion of the peripheral groove of a rotatable casting wheel, guided away from the peripheral groove, and returned on the same side of the casting wheel to the peripheral groove by a plurality of band guide wheels of substantially the same diameter and a band positioning wheel of smaller diameter than the band guide wheels is positioned adjacent the periphery of the rotatable casting wheel and arranged to press the flexible band into positive contact with the casting wheel, the improvement therein of the ratio between the thickness of the flexible band and the diameter of the band positioning wheel being lower than one to
 90. 2. The invention of claim 1 and wherein the thickness of the flexible band is in the range of from 0.0747 inch to 0.125 inch, and the diameter of the band positioning wheel is greater than 12 inches.
 3. The invention of claim 1 wherein the diameter of band positioning wheel is at least one-third as large as the diameter of the band guide wheels.
 4. The invention of claim 1 wherein the diameter of the band positioning wheel is sized to impart no more than three times the bending strain to the flexible band than the band guide wheels.
 5. The invention of claim 1 wherein the diameter of the band positioning wheel is sized to impart no more bending strain to the flexible band than the strain felt by the band as it passes about the casting wheel and is in direct contact with molten metal.
 6. In a machine for continuously casting metal wherein the inner surface of an endless flexible band partially about the peripheral groove of a casting wheel and about a tensioning wheel spaced from the casting wheel and a band positioning wheel is placed adjacent the casting wheel and engages the outer surface of the band urges the inner surface of the band into engagement with the casting wheel, the improvement therein of the ratio of band thickness to band positioning wheel diameter being smaller than one to
 90. 7. The invention of claim 6 wherein the band tensioning wheel diameter is greater than three times the positioning wheel diameter.
 8. The invention of claim 6 wherein the band positioning wheel is sized and arranged to impart no more than three timEs the bending strain to the flexible band than the tensioning wheel.
 9. The invention of claim 6 wherein the diameter of the and positioning wheel is sized to impart no more strain to the flexible band than the strain felt by the band as it passes about the casting wheel and is in direct contact with molten metal.
 90. 